Atlantic Oscillation (NAO) and the drought. In:
Assessment of the Regional Impact of Droughts in
Europe. Demuth, S. and Stahl, K.(eds). Final Report,
ARIDE. Institute of Hydrology, Freiburg, pp. 106–
ttir, J.F., Uvo, C.B. and Snorrason, A
Multivariate Statistical Analysis of Iceland River Flow
Series and Variability in Atmospheric Circulation. XXIII
Nordic Hydrological Conference, Tallinn, Estonia, 8–
12 August 2004. NHP Report 48,9985-56-921–0.
25. Snorrason, A
. 1990. Hydrological variability and
general circulation of the atmosphere. XVI Nordic
Hydrological Conference, NHK-90, Kalmar, Sweden,
29 July–1 August 1990.
26. Wedgbrow, C., Wilby, R.L., Fox, H.R. and O’Hare, G.
2002. Prospects for seasonal forecasting of summer
drought and low river flow anomalies in England and
Wales. Int. J. Climatol. 22, 219–236.
27. Wilby, R.L. 2001. Seasonal forecasting of UK river
flows using preceding North Atlantic pressure patterns.
J. Chartered Inst. Water Environ. Manage. 15, 56–63.
28. Wilby, R.L., Wedgbrow, C.S. and Fox, H.R. 2004.
Seasonal predictability of the summer hydrometeorol-
ogy of the River Thames, UK. J. Hydrol. 295, 1–16.
29. Kiely, G. 1999. Climate change in Ireland from
precipitation and streamflow observations. Adv. Water
Res. 23, 141–151.
30. Kaczmarek, Z. 2002. The influence of the North
Atlantic Oscillation on European river flow. In: The
North Atlantic Oscillation and Its Role in Climate and
Hydrology in Poland, 2002. Marsz, A.A. and Styszyn
ska, A. (eds.). Akademia Morska, Gdynia, pp. 163–172
31. Kaczmarek, Z. 2003. The impact climate variability on
flood risk in Poland. Risk Anal. 23, 559–566.
ska, A. 2002. Relationships between the Warta
River flow and winter NAO index in 1865–2000. In:
The North Atlantic Oscillation and Its Role in Climate
and Hydrology in Poland, 2002. Marsz, A.A. and
ska, A. (eds). Akademia Morska, Gdynia, pp.
173–180 (In Polish).
wka, D., Nieckarz, Z. and Pociask-Karteczka,
J. 2002. The North Atlantic Oscillation impact on
hydrological regime in Polish Carpathians. In: In-
terdisciplinary Approaches in Small Catchment Hydrol-
ogy: Monitoring and Research. FRIEND International
Conference, Demanovska Dolina, 25–28 September
2002, pp. 132–135.
34. Pociask-Karteczka, J., Limano
wka, D. and Nieckarz,
Z. 2002–2003. The North Atlantic Oscillation impact
on hydrological regime of Carpathian rivers (1951–
2000). Folia Geogr. Ser. Geogr. Phys. 33–34, 89–104 (In
Polish with English summary).
35. Pociask-Karteczka, J., Nieckarz, Z. and Limano
D. 2003. Prediction of hydrological extremes by air
circulation indices. Int. Assoc. Hydrol. Sci. Publ. 280,
36. Pfister, L., Humbert, J. and Hoffmann, L. 2002. Recent
trends in rainfall-runoff characteristics in the Alzette
River basin, Luxembourg. Climatic Change 45, 2, 323–
37. Stefan, S., Ghioca, M. and R^mbu, N. 2004. Study of
meteorological and hydrological drought in Southern
Romania from observational data. Int. J. Climatol. 24,
38. R^mbu, N., Boroneant, C., Buta, C. and Dima, M. 2002.
Decadal variability of the Danube River flow in the
lower basin and its relation with the North Atlantic
Oscillation. Int. J. Climatol. 22, 1169–1179.
39. R^mbu, N., Dima, M., Lohman, G. and Stefan, S. 2004.
Impact of the North Atlantic Oscillation and the El
o–Southern Oscillation on Danube River flow
variability. Geophys. Res. Lett. 31, 203–206.
40. Menduni, G., Baldi, M., Maracchi, G. and Meneguzzo,
F. 2004. The Arno River seasonal discharge as an index
of climate variability: trends and connections to the
larger scale variability. Geophys. Res. Abstr. 6.05257.
41. Rodriguez-Puebla, C., Encinas, A.H., Nieto, S. and
Garmendia, J. 1998. Spatial and temporal patterns of
annual preicipitation variability over the Iberian
Peninsula. Int. J. Climatol. 18, 299–316.
42. Trigo, R.M., Pozo-Vazques, D., Osborn, T.J., Castro-
Diez, Y., Ga
miz-Fortis, G. and Esteban-Parra, M.J.
2004. North Atlantic Oscillation influence on pre-
cipitation, river flow, and water resources in the Iberian
Peninsula. Int. J. Climatol. 24, 925–944.
43. Cullen, H.M. an d deMenocal, P.B . 2000. North
Atlantic influence on Tigris-Euphrates streamflow.
Int. J. Climatol. 20, 853–863.
44. Heidi, M., Cullen, H.M., Kaplan, A., Arkin, P. and
deMenocal, P.B. 2002. Impact of the North Atlantic
Oscillation on Middle Eastern climate and streamflow.
Climate Change 55, 315–338.
45. Rodwell, M.J., Rodwell, D.P. and Folland, C.K. 1999.
Oceanic forcing of the wintertime North Atlantic
Oscillation and European climate. Nature 398, 320–323.
46. Haarsma, R.J., Drijfhout, S.S., Opsteegh, J.H. and
Selten, F.M. 2000. The impact of solar forcing on the
variability in a coupled climate model. Space Sci. Rev.
Institute of Geography and Spatial
Department of Hydrology
Krakow, 30 387, Poland
Megacryometeors: Distribution on Earth and
The research of the historical record of ice
falls brings together many cases that are
apparently similar (1–3). Practically all
clear-sky ice falls were not appropriately
researched because they were routinely
assigned, without verification, to aircraft
icing processes, to wastewater from air-
craft lavatories (blue ice), or to the leakage
of aircraft water tanks. However, it is
important to take into account, first, that
documented historical references about
these events go back to the first half of
the 19th century, so many cases existed
before the invention of airplanes (1–3),
and second, that a detailed search of
scientific databases (Web of Science,
GeoRef) regardin g well-known a ircraft
icing processes revealed a lack of prece-
dents that corroborate that ice formation
on any part of aircraft can reach dimen-
sions of approximately 1 m and weights of
up to several hundred kilograms.
A simplistic analysis of these events as
a whole can thus lead to misunderstanding
because different types of ice falls corre-
spond to different formation scenarios in
the earth’s atmosphere, either natural in
the strict sense of the term, or with a direct
or indirect relation with human activities.
Consequently, it is necessary to define
differentiation criteria (e.g., texture, and
structural and compos itional character-
istics of the ice) to distinguish among them
(4). The term megacryometeor was recently
coined (5) for the following reasons: to try
to avoid terminological confusion; to
emphasize the existence of such atmo-
spheric phenomenon; and to describe large
atmospheric ice conglomerations that, de-
spite sharing many textural, hydrochem-
ical, and isotopic features detected in large
hailstones, are formed under unusual
atmospheric conditions that clearly differ
from those of the cumulonimbus cloud
scenario (i.e., clear-sky conditions).
The fall of large ice blocks (weighing
approximately 1 kg to hundreds of kilo-
grams) from the clear sky is one of the
most interesting (and controversial) issues
in the atmospheric sciences (6). Meaden
(6) used the term ice meteors to name them
and proposed that their origin had to be
different from that of large hailstones.
Later, Corliss (1) used the term hydro-
meteors. Corliss also differentiated them
from classic hailstones and suggested that
they have an atmospheric ori gin, but
different possible formation scenarios.
Probably the largest and most impressive
events of megacryometeors have occurred
in China, Brazil, and Spain. In 1995, an ice
block approximately 1 m in size fell in
Zhejiang, China (7). Some farmers wit-
nessed three large chunks of ice crash with
a whoosh into the paddies of Yaodou
village; the largest chunk left a crater
about a meter in diameter and a half-
meter deep. In Campinas and Itapira,
Brazil, two huge megacryometeors of 50
and 200 kg fell in 1997; the atmospheric
isotopic signature of both specimens was
unequivocally confirmed (8). Finally, on
21 July 2004, a huge mass of ice weighing
approximately 400 kg fell very close to
a 15-year-old girl in Toledo, Spain.
Our study of the rate of these earthfall
events indicates that mainly after 1950, the
number of hits has spectacularly increased,
and the hits occur over practically the
whole planet (3). From 2001 to April 2006,
a total of 46 ice-fall events have been
witnessed and recorded. Verifiable effects
include the megacryometeors’ crashing
through roofs or producing small impact
craters (i.e., La Milana, Soria, Spain, Fig.
1; Surrey, UK; Oakland, California, USA).
These impacts have occurred in Argentina,
Australia, Canada, Colombia, India, Ja-
pan, Mexico, New Zealand, Portugal,
Spain, Sweden, The Netherlands, the
United Kingdom, and the United States.
Fourteen ice falls occurred in 2005 alone;
these occurred in Japan, The Netherlands,
314 Ambio Vol. 35, No. 6, September 2006Ó Royal Swedish Academy of Sciences 2006
the United States, the United Kingdom,
and Spain, and the megacryometeors
weighed from about 0.5 kg to more than
5 kg. As of this writing, four documented
ice falls have been recorded in 2006, one in
India and three in the United States. The
two last known events, in April 2006 in
California (USA), produced a verifiable
small impact crater on the ground in
Oakland and a hole in the roof of
a gymnasium in Loma Linda (9, 10).
After 6 years of compilation and study
of ice events occurring all around the
world (10), together with the analysis of
megacryometeors that fell in Spain during
this period (Fig. 1), we are starting to
understand the textural features and the
hydrochemical and isotopic composition
of megacryometeors (11–14) (Fig. 2).
Megacryometeors’ textures include zones
of massive ice, large isolated cavities,
millimeter-sized oriented air bubbles, and
ice layering. Capillary electrophoresis
analysis, combined with traditional wet-
chemical (molecular ultraviolet and visi-
ble-light spectr ophotometry) o f m ajor
, and HCO
were performed by means of hydrostatic
injection (10 cm for 30 s) at 258C. Trace
, and NO
) were quanti-
fied effectively by electrokinetic injection
(4 kV, 10 s) at 158C. The results showed
variability in their chemical composition
patterns (13). Very recent isotopic studies
of megacryometeors confirm that d
) of all samples fall into
the meteoric water line (15), unequivocally
demonstrating that megacryometeors
match well with typical tropospheric val-
ues (14). Also, theoretical calcul ations
allow us to estimate that the vertica l
trajectory in effective growth of the mega-
cryometeors was lower than 3.2 km (14).
At present, no model is able to satis-
factorily explain what factors cause the ice
nucleation and gro wth, or how these
unusually large ice blocks can be actually
formed and maintained in the atmosphere.
Several hypotheses have been proposed
that posit both terrestrial (1, 11–14, 16)
and cosmic (17) causes. The possibility
that the source of the megacryometeor
water could be nonterrestrial was consid-
ered, but this possibility was ruled out
because as previously defined, the water
signature (25% . dD
(14) is clearly tropospheric (very different
from that reported for comets [þ1028% .
. þ862%]) (18). Crew (16)
proposed that gr eat masses o f w ater
(droplets and vapor) could be transported
up into the atmosphere by tornados, then
froze n and con verted into ice chunks.
Crew suggests the existence of some
atmospheric mechanisms that would avoid
Figure 1. (A) Megacryometeor in situ that fell in La Milana, Soria (27 January 2002). It landed near a startled farmer who was riding his tractor.
More than 16 kg of ice was recovered by the environmental police of the Guardia Civil (SEPRONA). The size of the small impact crater generated
by the megacryometeor was ’50 cm. (B) One of the fragments of the megacryometeor that fell in San Feliz de Lena (Asturias) (26 January 2000)
(artificial illumination to highlight its textural features).
Figure 2. Selected significant information about megacryometeors. The hydrochemical and
isotopic data corresponds to megacryometeors that fell in Spain. [(2-4, 11-14) and http://tierra.
redirs.es/megacryometeors]. Abbreviations in the figures are C, number of countries; LOD,
below the limit of detection; n, number of ice fall events; nd, not detected; (rc), average
concentration error; SMOW, Standard Mean Ocean Water.
Ambio Vol. 35, No. 6, September 2006 315Ó Royal Swedish Academy of Sciences 2006
dispersion and favor accretion of the ice.
Our studies indicate that during the period
in which the fall of megacryometeors to
earth occurred in Spain (mainly during 10–
17 January, 2000), anomalous atmospheric
conditions were observed to exist (12, 14):
a sudden drop in the tropopause occurred
over Spain. Atmospheric soundings from
NOAA were collected for the days before
and during the occurrence of the mega-
cryometeors in Spain. The analysis of the
soundings indicates that the tropopause
sank from a level of ’250 hPa (’10 500
m) on the days before the events, to a lower
level of ’400 hPa (’7000 m) on the days
of the events. This process was not
observed simultaneously at all st ations
and seems to have propagated from north-
west to east and then to the south. Along
with the amount of sinking, the other
significant factor is the accompanying
increase in humidity (near saturation but
with no condensation) observed in all
cases (except over Madrid). Ozone anom-
alies and wind shear were also found to
coexist with the tropopause undulations.
Only by use of an interd isciplinary
approach, including atmospheric and cli-
matic studies, simulation, and analysis of
physicochemical experiments of the icewill it
be possible to learn the real cause of
megacryometeors and the reasons for the
apparent multiplication of these objects (19).
References and Notes
1. Corliss, W.R. 1983. Ice falls or hydrometeors. In:
Tornados, Dark Days, Anomalous Precipitation and
Related Weather Phenomena: A Catalog of Geophys-
ical Anomalies. The Sourcebook Project, P.O. Box 107,
Glen Arm, MD 21057, pp. 40–44.
pez-Vera, F. 2000. Los
bloques de hielo que caen del cielo. Antecedentes y
a reciente. Rev. Educa. Cienc. Tierra. 8,
130–135 135 (In Spanish).
as, J. and Lo
pez-Vera, F. 2002. Grandes
bloques o meteoros de hielo. In: Riesgos Naturales.
Ayala-Carcedo, F.J. and Olcina Santos, J. (eds.). Ariel
Ciencia, Editorial Ariel, S.A., 1141–1148 (In Spanish).
4. Martinez-Frias, J. and Rodriguez-Losada, J.A. 2006.
Atmospheric mega cryometeor events ver sus small
meteorite impacts: scientific and human perspective of
a potential natural hazard. In: Comet and Asteroid
Impacts and Human Society. Brobovsky, P. and Rick-
man, H.(eds.). ICSU. Springer. (in press).
5. Martinez-Frias, J. and Travis, D. 2002. Megacryome-
teors: fall of atmospheric ice blocks from ancient to
modern times. In: Environmental Catastrophes and
Recovery in the Holocene. Leroy, S. and Stewart,
I.S.(eds.). Brunel University, West London, UK, pp.
6. Meaden, G.T. 1977. The giant ice meteor mystery. J.
Meteor. 2, 137–141.
7. Parker, J. 1995. (http://www2.jpl.nasa.gov/sl9/news56.
8. Pinto, H. 1997. Segundo relato
rio sobre o fenoˆ meno da
queda de blocos de gelo provenientes da atmosfera nas
oes de Campinas e de Itapira, NO Estado de Sa
Paulo, Brasil. (http://www.cpa.unicamp.br/gelo/gelo.
as, J., Lo
pez-Vera, F., Garcı
a, N., Delga-
do, A., Garcı
a, R. and Montero, P. 2000. Hailstones
fall from clear Spanish skies. Geotimes (June): 6–7.
as, J., Milla
n, M., Garcı
a, N., Lo
F., Delgado, A., Garcı
a, R., Rodrı
Reyes, E., Martı
, J.A. and Go
2001. Compositional heterogeneity of hailstones: atmo-
spheric conditions and possible environmental implica-
tions. Ambio 30, 450–453.
13. Santoyo, E., Garcı
a, R., Martı
as, J., Lo
Vera, F. and Verma, S.P. 2002. Capillary electropho-
retic analysis of i norganic a nions i n atmospheric
hailstone samples. J. Chromatogr. A 956, 279–286.
14. Martinez-Frias, J., Delgado, A., Millan, M., Reyes, E.,
Rull, F., Travis, D., Garcı
a, R., Lo
pez-Vera, F. et al.
2005. Oxygen and hydrogen isotopic signatures of large
atmospheric ice conglomerations. J. Atm. Chem. 52,
15. Craig, H. 1961. Isotopic variations in meteoric waters.
Science 133, 1702–1703.
16. Crew, E.W. 1977. Fall of a large ice lump after a violent
stroke of lighting. J. Meteor. 2, 142–148.
17. Foot, R. and Mitra, S. 2002. Ordinary atom-mirror
atom bound states: a new window on the mirror world.
Phys. Rev. D66, 061301.
18. Deloule, E., Robert, F. and Doukhan, J.C. 1998.
Interstellar hydroxyl in meteoritic chondrules: implica-
tions for the origin of water in the inner solar system.
Geochim. Cosmochim. Acta 62, 3367–3378.
19. Thanks to Dr. David Hochberg for his revision and
correction of the English-language version of this
article. Also thanks to CSIC and ICSU for their
Planetary Geol ogy Laboratory
Centro de Astrobiologia, Ctra de Ajalvir,
km. 4 28850 Torrejo
n de Ardoz
Antonio Delgado Huertas
Department of Earth Sciences and
Environmental Chemistry Estacio
Experimental del Zaidı
n, CSIC Prof.
Albareda 1 18008 Granada, Spain
Ecological Economic Problems and
Development Patterns of the Arid Inland River
Basin in Northwest China
The inland river basin in arid Northwest
China is located in the center of the
Eurasian continent, north of 358N and
west of 1068E, occupying 24.5% of China’s
total land area, and it is one of the most
arid regions in the world (1). This region is
characterized by alternating bands of
relatively humid mountains and arid
plains. Several rivers, such as the Heihe,
Shiyang, Shule, and Tarim, originate in
the mountainous regions, nourish some
oases in the middle reaches, and then flow
to small lakes or disappear in the large
arid desert plain. Alternating mountains,
oases, and desert is the typical landscape
pattern of the arid inland river basin in
Northwest China. Although there is more
agricultural and animal husbandry pro-
duction in these basins than in other arid
regions, water resources are the most
significant factor restricting basin devel-
opment (2). We take the Heihe River Basin
as a case to focus on some critical
ecological economic problems that have
recently arisen in the inland river basin,
and we put forward a sustainable de-
velopment pattern according to the system
The Heihe River Basin (HRB), the second
largest inland river basin in arid North-
west China, is located between 97842
1028E and 37841
N. It covers an
area of approximately 128 000 km
main stream of the Heihe River, with
a length of 821 km, originates in the Qilian
Mountians, flows through the Hexi corri-
dor of Gansu Province, and enters into
two terminal lakes (Fig. 1). The landscape
and human production are very different
in the HRB. In the upper reaches of the
HRB, mountain grassland and forest are
the main landscape types, and desert
grassland is the main landscape type in
its lower reaches. Therefore, the main
human production in the upper and lower
reaches of HRB is animal husbandry
based on mountain grassland and desert
grassland. In the middle reaches of the
HRB, irrigation oases are distributed
along the sides of the Heihe River.This is
a productive zone of economic develop-
ment for the entire HRB: 88.47% of the
HRB population lives here, and 87.93% of
the HRB GDP are focused here. It is one
of the major grain-producing regions in
China. However, because water utilization
intensity is continuously increasing in the
oases located in the middle reaches of the
HRB, the discharge of water into the lower
reaches of the river has decreased signifi-
316 Ambio Vol. 35, No. 6, September 2006Ó Royal Swedish Academy of Sciences 2006